A. Field of the Invention
The present invention is directed to magnetic head sliders used in hard disk drive (HDD) head gimbal assemblies. More specifically, the present invention pertains to producing micro-texture on a slider substrate using chemical & mechanical polishing techniques.
B. Description of the Related Art
Presently, the hard disk drive industry is observing great success in the consumer electronics environment. One of the main reasons for this success is the ability to achieve ever increasing storage capacity reflecting consumer demand in ever decreasing form factors (e.g., greater than 1 Gb in 1″ disks and below for portable music players). So far, these advancements are being achieved with minimal cost compared to competitors (e.g., flash memory).
However, continuing these advances require overcoming arising design and manufacturing difficulties. These difficulties can be found both in the drive level and the component level.
By way of background, while executing a read/write instruction, an actuator (arm) of a disk drive operates to position a magnetic head along the surface of a rotating disk. Typically, this magnetic head is supported on a slider. A typical slider body is shown in FIG. 1. As shown in FIG. 1, an ABS 102 design known for a common slider 104 may be formed with a pair of parallel rails 106 and 108 that extend along the outer edges of the slider surface facing the disk. The two rails 106 and 108 typically run along at least a portion of the slider body length from the leading edge 110 to the trailing edge 112. The leading edge 110 is defined as the edge of the slider that the rotating disk passes before running the length of the slider 104 towards a trailing edge 112. The transducer or magnetic element 114 is typically mounted at some location along the trailing edge 112 of the slider as shown in FIG. 1.
The operation of a typical slider is shown in FIG. 2. A suspension 204 holds the head gimbal assembly (HGA) 202 over the moving disk 206 (having edge 208) and moving in the direction indicated by arrow 210. In operation of the disk drive, as shown in FIG. 2, an actuator 212 moves the HGA over various diameters of the disk 206 (e.g., inner diameter (ID), middle diameter (MD) and outer diameter (OD)) over arc 214.
In order to continue the current advances in disk drive technology, two main design criteria must be continuously addressed and improved upon: a) the flying height and b) the surface roughness of the various disk drive components, while maintaining optimum flying characteristics of the head (e.g., crown, camber, twist, and overcoat and pole tip recession).
In order to achieve maximum hard disk drive performance, the head must fly as close to the surface of the disk as possible while still maintaining a consistent, required spacing. This spacing is also known as the “flying height” or “magnetic spacing” of the disk. When a disk is rotated, it carries with it a small amount of flowing air (substantially parallel to the tangential velocity of the disk) on its surface that acts to support a magnetic head flying above, thereby creating the “flying height” of the head above the disk. Typically, the slider supporting the head is aerodynamically shaped to use the flow of this small amount of air to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from contacting the disk. The surface of magnetic head closest to the disk (and being supported by the flowing air) is referred to as the “air bearing surface”. In FIG. 1, the rails 106 and 108 form the air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the slider rails 106 and 108. As the air flow passes beneath the rails 106 and 108, the air pressure between the rails and the disk increases thereby providing positive pressurization and lift. In general, as the air bearing surface area increases, the amount of lift created is also increased. Therefore, as a design criterion, there is a need for a method that allows for design of a flying height constituting the minimal amount of spacing between the head and the disk required for successful operation of the hard disk drive.
Second, any surface roughness issues must be addressed to overcome any associated friction issues that might impede the head's ability to fly as close to the surface of the disk as possible. Along with general frictional resistance due to the moving parts of the disk drive (e.g., the disk, the loading/unloading zones or the magnetic head), excessive surface roughness of either the disk or the magnetic head significantly increases the chances of HDI (head disk interaction), often resulting in intermittent contact and/or crashes. However, while it is possible to smoothen these surfaces, continuously increasing the smoothness comes with problems as well. Smoother surfaces lead to increased inter-molecular (Van der Waal's) forces acting at the interface and higher sensitivity to altitude and pressure changes during operational mode. Both of these factors may cause increased undesired variations in the flying height. Therefore, there is a need for a cost-effective process that can easily attain the desired smoothness of the disk designed for optimum performance.
The flying height and the surface roughness of the disk drive components must be designed to preserve the mechanical operating parameters of the head, such as crown, camber and twist. The “crown” represents a deformation in shape along forward and aft directions of the slider (as shown by the Y-Y plane), and the “camber” represents a deformation in shape along lateral directions of the magnetic head slider (as shown by X-X plane). Crown and camber are shown in FIG. 3. Also, while achieving the desired value of micro texture on the substrate, the overcoat recession and pole tip recession characteristics of the head must be optimal as well. Overcoat recession is the difference in height between the surface of the alumina of the head and the air bearing surface. Pole tip recession is the difference in height between the pole tip material and the air-bearing surface.
Generally, grinding and lapping are processes by which the head is smoothened and finished. Specifically, grinding is a process of material removal in which a surface composed of many hard abrasive grits wears away a softer material. Lapping is a manufacturing method that employs particles of an abrasive material (often in liquid form) to remove undesired stock from a surface.
Several attempts have been made to address these issues both at the disk and head level. For instance, a certain amount of texturing may be designed in at the loading/unloading areas (i.e., “zone texturing”) in order to reduce the effects described above. However, it proves to be an insufficient and inefficient method for achieving desired performance.
Another option can be to increase the roughness of the disk as shown in FIG. 4a. FIG. 4a shows a smooth slider body surface flying above a textured disk surface. However, again as discussed above, increasing roughness in such a manner may become an issue when the increased roughness leads to greater friction, thereby creating a greater-than-required flying height. Moreover, increasing the surface roughness of the disk (being the data carrier) is generally not favored. Another alternative for increasing surface roughness for optimal performance is the texturing of the slider body itself as shown in FIG. 4b. FIG. 4b shows a textured slider body surface and a smooth disk surface.
Generally, a slider body may be comprised of a two-phase granular composite ceramic material called AlTiC (Aluminum Titanium Carbide), wherein the AlTiC is formed by distinctive grains of Al2O3 (aluminum oxide) and TiC (titanium carbide). The head portion of the slider typically is a thin layer of alumina fabricated on the trailing edge face of the slider portion in which the magnetic portion of the head is embedded. FIGS. 5a-b illustrate in a top and side view of one embodiment of a slider 504. The substrate 502 may then be deposited with an undercoat material 504 of sputtered transparent alumina. The shield 506 and read/write sensor 508 may be built onto the sputtered transparent alumina using conventional photolithographic and electro deposition techniques. The read/write sensor 508 may then be carefully deposited with the overcoat material 510 (also alumina), which also serves as a dielectric medium encasing the read/write sensor 508 of the head.
However, it is often the alumina portion of the slider that if not designed correctly, comes in contact with a disk, thereby causing failure. The overextension of the overcoat of alumina is generally the result of improper lapping. Therefore, it is primary design goal to ensure that, regardless of the operating conditions of the slider, the height of any alumina along the trailing edge of a slider not be above height of the air bearing surface of the slider.
A method for texturing the slider body is suggested in “Method and Apparatus for Ultrasonically Texturing ABS of Magnetic Head of Hard Disk Drive” (U.S. Pat. No. 5,967,880). In this method, ultrasonic energy in the form of a sonitrode is used in combination with an abrasive alumina slurry to produce a micro-texture on the slider body. In particular, the head is juxtaposed with the disk, and an abrasive slurry is disposed there between. Finally, the sonitrode is vibrated to created a texturing along the air bearing surface of the head. However, this method has its limitations. First, the use of the vibrations from the sonitrode along the surface of the head creates manufacturing irregularities and any excess jarring of the slider body may diminish the performance of the head. Secondly, as the abrasive slurry particles collide with the body, the particles often fuse to the slider body. This fused abrasives are practically impossible to remove, leaving behind foreign bodies embedded in the slider. Consequently, the probability of interference in proper flying height characteristics is largely increased, the amount depending on the size and amount of the abrasive slurry fused to the head. This interference, when sufficient, can result in catastrophic failures during drive level operation.
A third, alternative approach practiced in today's industry is the use of an etching process to create the composite used to form the slider body material (e.g., the two phase composite of Al2O3 and TiC discussed above). Alumina grains may be preferentially etched over the granular composite material to create relative differences in the heights of the two grains, thereby creating a micro-texture shown in FIG. 6a-b. This micro texture produced with this technique is due to the difference in the etch rate of the two materials. However, since this method uses an ion beam applied to the surface of the slider, there is a risk of exposing the sensitive elements of the reader to the high energy of the ion beam (as shown in FIG. 7). The amount of texture created is directly proportional to the time the composite is exposed the energy beam. However, when a reader is exposed to a excessive amount of energy, it begins to show signs of magnetic degradation. One approach to negating the effects of the energy beam is to cover the sensitive reader elements with a photo resist (as shown in FIG. 8), and then subjecting it to the beam. However, this creates further complications in the fabrication process, and degrades magnetic head performance.
Another approach has been discussed in “Method for Producing Sliders” (U.S. Pat. No. 6,428,715), disclosing a method for removing alumina protrusion wherein the air bearing surface of the slider is treated with an aqueous base having a pH of approximately 9-11. However, this method is disadvantageous from a manufacturing point of view, as the etching process disclosed requires actually immersing the selected elements in the aqueous solution. The process is both imprecise and not cost-efficient.
Another method described in “Method and apparatus for the manufacture of thin film magnetic transducers using a compliant, soft lapping process” (U.S. Pat. No. 6,712,985), discloses a chemical-mechanical process entailing the use of a lapping media slurry in conjunction with a soft compliant pad. The lapping media is then applied to the surface of the head using the soft compliant pad. Upon application, the motion of the compliant pad allows the mechanical etchants to eliminate anomalies between the magneto-resistive sensor element of the head and the shields. However, this process is limited by its imprecision in the applications of the slurry, and is generally directed towards the elimination of anomalies and smears, not towards the creation of a micro texture on a slider body.
Conventional lapping processes typically use diamonds as the mechanical abrasive found in the slurry used to create the finished surface. Diamond, being very hard relative to the magneto-resistive sensor and the adjoining shields, upon contact leaves behind residual stress points which diminish the magnetic performance of the head. There is a need for a method which utilizes a much softer abrasive in order to avoid the residual stress points left behind. Moreover, lapping with a diamond slurry often causes the surface of the magnetic head to become scratched thereby diminishing the magnetic head performance. Lastly, lapping with the embedded diamond particles found in the diamond slurry often leaves behind markings (commonly referred to as “black spots”) on the magneto-resistive sensor and shield areas.
Therefore, it is evident that there is a need for a developing a new method overcoming the aforementioned deficiencies and producing an optimum amount of micro-texture to be precisely fabricated on a slider substrate in a cost-efficient manner.